Characterization of voltage-gated and calcium-activated potassium currents in toadfish saccular hair cells

Patch clamp methods were used to study calcium activated (IKCa) and voltage-gated (IK) potassium currents in enzymatically disassociated hair cells from the saccule of the toadfish Opsanus tau. In one population of hair cells, tetraethylammonium bromide (TEA) blocked all outward current, leaving only an inward calcium current (ICa). This current blocked by TEA was also blocked by barium (5 mM) and cadmium (0.2 mM) but only partially blocked by zero external calcium. In the majority of the cells, after TEA (25 mM) was used to block IKCa, a second outward current remained. This current was resistant to block by apamin, barium (5 mM) and cadmium (0.2 mM). Its kinetics of activation and deactivation were considerably slower than those of IKCa. Because of the current/voltage characteristics, its resistance to block by the above agents and voltage-gated activation, this current was termed IK. Study of the rates of activation and deactivation of the two currents in hair cells exhibiting either fast or slow total outward current activation showed that these two kinetic parameters were linked in a cell, i.e., cells with fast IKCa kinetics exhibit faster IKCa kinetics than cells with slower IKCa kinetics. Cell attached and inside out recordings showed a high conductance channel with short open times and a lower conductance channel with longer open times active over the same voltage ranges as those seen in whole cell recordings. Since these two currents with quite different but linked kinetics are active over the same voltage range, their co-existence may be of some importance to sensory coding in the hair cells.